DURANGO, Colo.—President Barack Obama has signed a proclamation creating a national monument at the dramatic rock formation in southwestern Colorado on a site that was home to the ancestors of modern Pueblo Indians 1,000 years ago.

The proclamation signed Friday preserves nearly 5,000 acres of high desert at Chimney Rock, which holds spiritual significance for some tribes. It bars sale or lease of land by current property owners while protecting existing property rights, giving the government time to acquire private property inside the boundaries.

The president called the monument a national treasure with deep cultural and educational value.

The move has bipartisan support and comes as Obama is locked in a tight race with GOP presidential candidate Mitt Romney in the swing state.